1. Field of the Invention
This invention relates to vehicle diagnostic method and an apparatus therefor, and in particular, to the vehicle diagnostic method and apparatus for communicating with an electronic control unit mounted on a vehicle to diagnose the vehicle based on the communication results. More specifically, it relates to the vehicle diagnostic method and apparatus, in which a forced activation signal is issued so that each part of the vehicle will show an expected state, whereby each diagnostic item is judged to be good or bad based on whether or not an actual state of the part is in the expected state.
2. Description of the Related Art
To improve engine control functions, an electronic control unit (ECU) with a microcomputer has been used in recent years for executing control programs, such as control of ignition timing in an engine, control of valve opening and closing timing, and/or control of fuel injection in an electronic fuel injector (EFI) for an automobile (hereinafter, referred to as a "vehicle"). The ECU is connected to sensors, such as a temperature sensor for detecting a temperature of engine cooling water, an engine-speed sensor for detecting an engine speed, a vehicle-speed sensor for detecting a vehicle speed, an 02 sensor for detecting an oxygen concentration in exhaust gas, and various switches including a brake switch for detecting that a driver has stepped on a brake pedal. The ECU thus executes various kinds of controls based on detection signals output from the sensors and others.
On the production line where vehicles with such an ECU are manufactured, in the final test process after assembled, it should be diagnosed whether or not each of sensor and the like, and the ECU itself functions normally. For example, Japanese patent publication No. Hei 3-59372 proposes a diagnostic method in which a diagnostic apparatus with a microcomputer executes a vehicle diagnostic program to diagnose a desired diagnostic item at scheduled timing.
In a failure diagnosis related to a plurality of diagnostic items, for example, as disclosed in Japanese patent publication No. Sho 61-25091, the plurality of diagnostic items are diagnosed in predetermined order and the results of pass/failure or displayed judgment in respective diagnostic items are output one by one on a display device.
Some of such vehicle diagnostic items require particular preconditions. For example, an "Ne Diagnosis" to determine whether or not an engine speed Ne at idling time is in a given range or not must be executed under the condition that the engine has been warmed up adequately. Some other diagnostic items require no precondition and are allowed to complete the diagnosis for an instant, such as a "Brake Switch Diagnosis" to diagnose an opening and closing function of a brake switch.
When such a plurality of diagnostic items are required, the sequence of items to be diagnosed is predetermined in a conventional vehicle diagnostic program. It is therefore impossible to diagnose a subsequent item before the previous item is diagnosed as being passed or failed. If the "Brake Switch Diagnosis" is prearranged to be executed after the "Ne Diagnosis", for example, the operator can not start executing the "Brake Switch Diagnosis" until the "Ne Diagnosis" has been completed after warming up the engine, and is kept waiting wastefully during the execution of the "Ne Diagnosis". This causes long compulsory working-hours of the operator.
To solve such problems, a diagnostic method may be available in which the diagnoses repeatedly circulates in a very short period of each execution cycle regardless of the pass or fail results, so that a diagnostic item or items that remain judged not to be passed after scheduled time has elapsed are diagnosed as being failure. In using such a circulating diagnostic method, the diagnostic period may be set such that one cycle of all the diagnostic processes is completed, for example, while the operator steps on the brake pedal. In this case, the "Brake Switch Diagnosis" is executed without fail while the operator steps on the brake pedal regardless of the sequence and timing of stepping the brake pedal. This makes it possible to reduce limits on the sequence and timing of operations to be performed for each diagnostic item, and hence to improve efficiency of work remarkably.
However, for example, a diagnosis of a function for controlling valve opening and closing timing in accordance with such parameters as the vehicle running speed and the engine speed, and a diagnosis of an evaporation system for collecting fuel gas evaporated from a fuel tank and supplying it to the engine when predetermined operating conditions are satisfied (hereinafter, referred to as an "EVP Diagnosis") are very difficult to be carried out, because it is difficult to realize such running condition in a limited diagnostic process or environment that said function and the evaporation system actually operate. For diagnoses related to such diagnostic items, a diagnostic technique may be available in which the ECU supplies a forced activation (energizing) signal to each associated part to forcibly actuate the valve or evaporation system so as to diagnose it as being good or bad based on whether or not a state actually obtained is in a state predicted corresponding to the forced activation signal.
However, the ECU is not able to issue plural forced activation signals at a time because of its restricted functionality, and the contents and destination of each forced activation signal vary depending on the diagnostic target. Therefore, when plural diagnostic items require respective forced activation signals, it is necessary first to issue a first forced activation signal for a first diagnostic item, and stop the first forced activation signal and then to issue a second forced activation signal for a second diagnostic item after completion of the first diagnosis. Thus, the second forced activation signal cannot be issued until completion of the diagnosis of the first item, and this causes a problem that diagnoses of the other items cannot be executed unless the diagnosis of the first item passes.
Even if only one diagnostic item requires issue of a forced activation signal and the other items do not require such signals, a concentration of the fuel in mixed gas may increase when the evaporation system is forcibly actuated by the forced activation signal. In such a case, if a diagnosis item or items susceptible to the fuel concentration in the mixed gas are included as other diagnostic items, these diagnostic items cannot be diagnosed correctly.